The present invention relates to a method and arrangement for controlling the flue duct draft effect (the chimney draft) upon an upstream exhaust gas cleaning system.
Recently, it is acceptable to operate exhaust gas cleaning systems without reheating the clean gas that leaves the scrubber unit, and to use wet systems as flue ducts. As a result, on the one hand the overall manufacturing costs, and on the other hand the maintenance cost, of the exhaust gas cleaning system can be significantly reduced. For inspection and repair of the components of the exhaust gas cleaning unit, especially in the scrubber, after shutting the boiler down one must take care that the chimney draft in the system components that are to be cleaned or repaired is substantially interrupted or discontinued. This is conventionally accomplished by suitable dampers or other closure elements that are permanently or temporarily installed into the feed and/or discharge lines (DE 34 01 922 A). Fixedly installed closure elements, such as dampers or the like, form additional resistances in the lines and are themselves susceptible to disruption and vulnerable to repairs. Closure elements that are temporarily installed into the line draft, for example balloons that can be inflated from the outside, cannot adequately and reliably absorb the differential pressures and loads that occur in lines having large cross-sections, and/or they require a relatively high installation expenditure.
It is an object of the present invention to make available a more rapid and easier dynamic sealing/opening of the air passage cross-section in order to regulate the draft effect of the flue duct upon an upstream exhaust gas cleaning system.
Pursuant to the inventive method, one allows a downwardly open flue duct to extend into a vat in such a way that, with the aid of a liquid (e.g. condensate) that collects in the vat, a liquid barrier that closes off a flue gas end of the flue duct relative to the environment is formed. To relieve the upstream exhaust gas cleaning system from the flue duct draft effect (chimney draft), at least a portion of the cross-section of the flue duct is exposed by lowering the level of the liquid below the edge of the flue duct.
The arrangement for controlling the draft effect of a flue duct upon an upstream exhaust gas cleaning system is inventively characterized in that a downwardly open flue duct can be immersed into a vat; in that by means of a liquid collected in the vat, a liquid barrier that closes off a flue gas end of the flue duct relative to the environment is formed; and in that the level of the liquid can be lowered below the edge of the flue duct to thereby expose at least a portion of the cross-section of the flue duct in order to relieve the upstream exhaust gas cleaning system from the flue duct draft effect.
By means of the invention, a flue duct or chimney draft through the components of the exhaust gas cleaning system can be reliably avoided during inspection and repair, and the condensate can be reliably withdrawn. The lowering of the level of the liquid or condensate can be realized in a straightforward and rapid manner by removing, e.g. draining, the liquid from the vat until the flue duct is no longer immersed in the liquid. With this procedure, the cross-section of the flue duct, or possibly a partial cross-section, is exposed from below.
DE 23 46 515 B discloses compensating for temperature-dependent changes in length of flue ducts by using immersion compensators. The lower end of a steel flue gas duct has three concentric tubular sections that are closed off at the top relative to one another and form narrow yet deep annular chambers. The central tubular section extends into a narrow, deep annular cup that is filled with heavy oil. The liquid barrier that is formed thereby is not suitable for regulating the flue duct draft effect.